Needle-Free Injections Perfected Using Supersonic Liquid Microjets

A new technique for firing liquid microjets through human skin is set to revolutionise drug delivery

October 11, 2012

Injections are an important and inevitable lynchpin of modern medicinal techniques. The idea is to force liquid directly into the body using a hollow needle to penetrate the skin. Without these kinds of jabs, the medical landscape would be inestimably poorer.

But injections have a number of downsides. They are an important source of disease transmission, particularly when needles are re-used and in the event of needle-stick injuries to health professional, they are painful and the needles are difficult and dangerous to dispose of. Then there’s needle phobia and so on.

So biomedical engineers, doctors and patients have dreamed of finding a better way–needle-free injections akin to Star Trek’s hypospray administered so ably by Dr McCoy.

There have been no shortage of attempts, some of which even predate the Star Trek series. The idea is that if the liquid is directed at the patient with enough force, it will penetrate the skin and force its way into the body.

Various groups have attempted this using compressed air and various kinds of liquid pumps but none have been particularly successful. One problem is that liquid jets can be just as painful as needles and even more damaging to the skin and tissue below.

But the most serious problem is splashing. In all of the techniques tried so far, some of the liquid splashes off the skin or doesn’t penetrate deeply enough and this makes it impossible to know what dose the patient has received. That’s a serious problem for any condition that requires a precise volume of drug – and that’s pretty much all of them.

This looks set to change. Today, Yoshiyuki Tagawa at the University of Twente in The Netherlands and a few pals say they’ve solved this problem thanks to a new technique for focusing a stream of liquid into a microjet travelling at up to 2000 miles per hour (850 m/s). Yep–that’s 2000 mph about the same speed as a supersonic Blackbird SR-71.

The technique is fairly straightforward. These guys fill a capillary with liquid and focus a laser pulse onto one end. This rapidly heats a portion of the liquid causing it to evaporate suddenly and send a shock wave through the tube. This pushes accelerates the rest of the liquid forcing it out of the capillary at high speed.

The tube and rate of heating is designed to generate shockwaves that focus this microjet so that its tip is just a few tens of micrometres across, smaller than a mosquito’s proboscis.

When the liquid hits the skin at this speed, the microject easily penetrates, delivering a precise volume of liquid to the tissue beneath. And all this happens with little, if any, splashing.

Tagawa and co have tested their system on gelatin covered with synthetic skin and say it works well as the images above seem to testify. “The results…take needle-free injections a step closer to widespread use,” they say.

Of course, there are significant steps ahead. One concern is that the laser pulse, as well as the heat and shockwave it generates, might damage certain types of drug. The tests so far have involved only water tinted with red-dye, so that will need to be examined carefully.

Another engineering problem is the design and manufacture of a robust device that will have wide utility without clogging. Needle-free injections will certainly be useful in modern hospitals and surgeries but the developing world has the most to gain.

And finally, the technique will need to be tested on a wide range of people. It’s possible that the microjets will have to be fine-tuned to cope with different skin types so that the drug volume delivered to young man with skin like elephant leather is the same as the dose received by an elderly lady with skin like tissue paper.

Needle-free injections are of huge potential benefit to the millions of people such as diabetics who live with a daily routine of multiple injections. For them, it’s a development that can’t come soon enough.